The Invention relates to a recording arrangement for recording an information signal in tracks on a record carrier, the recording arrangement comprising
an input terminal for receiving the information signal,
channel encoding means for channel encoding the information signal so as to obtain a channel signal suitable for recording in a track on said record carrier,
writing means for writing the channel signal in the track, the channel signal comprising subsequent or a succession of signal blocks, each signal block comprising a first block section which comprises a synchronization signal and a second block section which comprises a number of channel bytes, to a record carrier obtained with the recording arrangement, and to a reproducing arrangement for reproducing the information signal from the record carrier.
A recording arrangement as given in the opening paragraph is known from EP-A 492, 704, document (1) in the list of references that can be found at the end of this application.
The known arrangement is a recording arrangement of the helical scan type, such as used in a digital VCR (DVCR) and records an information signal comprising a digital audio signal and a digital video signal in audio signal recording sectors and video signal recording sectors respectively in subsequent tracks, where, when recording a track, the video signal recording sector in a track comes first and is followed by the audio signal recording sector. The order in which the sectors occur in a track can however also be in the reverse order. Further, other sectors may be included in a track, such as a clock run-in area located at the beginning of a track, so as to enable a locking-in of the internal system clock on the signals read from the track, and preamble and postamble areas that are located between the various sectors and function as an edit gap. Reference is made in this respect to the earlier filed European patent applications No. 93.202.950, reference (2) in the list of references, and No. 93.201.263, reference (3) in the list of references.
The prior art reference documents relate to proposals for the realization of a new digital video cassette (DVC) recorder standard, which enables the recording and reproduction of digital video and digital audio on/from a longitudinal magnetic record carrier such as magnetic tape. This new digital video recorder standard will lead to new digital video recorders/reproducers of the so-called DVC type.
The invention aims at providing a recording arrangement which is capable of recording other types of information signals in the known tape format as defined in the preamble. The recording arrangement in accordance with the invention is characterized in that the information signal is an MPEG information signal in accordance with an MPEG format, the MPEG information signal comprising subsequent or a succession of transport packets, that the channel encoding means are adapted to store each time information included in x transport packets of the MPEG information signal in the second block section of a group of y signal blocks of the channel signal, that the second block section of at least the first signal block of the group of y signal blocks comprise a third block section for storing identification information identifying the signal clock as being the first signal block of the group of y signal blocks, and that x and y are integers such that x∃1 and y∃1. More specifically, the recording arrangement in accordance with the opening paragraph is characterized in that the information signal is an MPEG information signal in accordance with an MPEG format, the MPEG information signal comprising subsequent transport packets, that the channel encoding means are adapted to store each time information included in x transport packets of the MPEG information signal in the second block sections of a group of y signal blocks of the channel signal, that the second block sections of the signal blocks comprise a third block section for storing sequence number information relating to a sequence number of the signal blocks, and that x and y are integers such that x∃1and y∃1.
The invention is based on the following recognition. The draft Grand Alliance HDTV System Specification dated Feb. 22, 1994, document (4) in the list of references, more specifically chapters V and VI of the specification, comprises a description of a transport system for transmitting an MPEG information signal, which includes a data compressed digital video signal and a corresponding data compressed digital audio signal, for broadcasting purposes or for transmission via a cable network. The MPEG information signal is in the form of transport packets having either an equal length or a variable length in time. In both cases, however, a transport packet comprises 199 bytes of information, the first byte of which being a synchronization byte.
A transmission such an MPEG information signal in the form of a recording on a reproduction from a record carrier, such as a magnetic record carrier as a tape, require special measures to be taken in order to realize such kind of transmission via the known tape format. More specifically, the invention relates to storing the transport packets in the signal blocks of the known tape format.
Generally, it can be said that, when storing the information included in a number of x transport packets of the MPEG information signal in a number of y signal blocks, some unoccupied space remains available in the y signal blocks for the storage of additional information, which additional information relates to the specific application of recording and reproducing the MPEG information signal on/from the record carrier. In a specific example of the DVC format, the second block sections of five signal blocks. Now, 11 bytes (=5xc3x9777xe2x88x922xc3x97187) remain available in the five signal blocks. Those 11 bytes can be divided over the second block sections of the five signal blocks in various ways so as to obtain the third block sections. One such way is that the first two bytes of all second block sections are available as third block sections and that the last byte available can be considered as a third block section to indicate the boundary between the information of the two transport packets as stored in the five signal blocks.
In the above example, identification information identifying the signal block as being the first signal block of the group of y signal blocks can be stored in a third block section of the first signal block in a group of y signal blocks. Or, sequence number information (sequence numbers) relating to the sequence of the signal blocks can be stored in the third block sections. This sequence number can also be identified as a continuity counter. The measures proposed result in a number of advantages.
The advantage of using identification information identifying a signal block as being the first signal block in a group of y signal blocks, is that the beginning of a group can be detected, which simplifies the read-out of the data during reproduction.
One advantage using sequence numbers is that, when reproducing the signal blocks, it can be decided upon retrieval of the sequence numbers, whether a signal block has been missed because of reproductions errors or not, so that an error correction or concealment can be carried out. Another advantage is that one may shuffle the information to be stored in the signal blocks upon recording. Upon retrieval of the sequence numbers it is possible to realize a corresponding deshuffling in response to the sequence numbers retrieved so as to obtain the original data stream.
Further, having sequence numbers included in the third block sections of the signal blocks makes it possible to repeat signal blocks in the case that a transport packet of the MPEG data stream stored in those signal blocks requires a higher protection against errors that can occur during the recording and a subsequent reproduction process.
The recording arrangement as given in the opening paragraph may also be characterized in that the information signal is an MPEG information signal in accordance with an MPEG format, the MPEG information signal comprising subsequent transport packets, that the channel encoding means are adapted to store each time information included in x transport packets of the MPEG information signal in the second block sections of a first group of y first signal blocks of said signal blocks of the channel signal so as to enable a normal play mode using video information stored in said first group of y first signal blocks during a normal play reproduction mode, the channel encoding means further being adapted to retrieve a trick mode video signal from the MPEG information signal and being adapted to store said trick or feature mode video signal in second block sections of a second group of z second signal blocks of said signal blocks of the channel signal so as to enable a trick play mode using the video information stored in said second signal blocks, that the second block sections of at least one signal block in each first and second group of first and second signal blocks respectively comprise a third block section for storing identification information indicating whether the group comprises first signal blocks or second signal blocks, and that x, y and z are integers such that x∃1, x greater than 1 and z greater than 1.
More specifically, the information signal is an MPEG information signal in accordance with an MPEG format, the MPEG information signal comprising subsequent transport packets, that the channel encoding means are adapted to store each time information included in x transport packets of the MPEG information signal in the second block sections of a group of y signal blocks of the channel signal, that the second block sections of at least those signal blocks in a group of y signal blocks that comprises the start portion of a transport packet comprise a third block section for storing sequence number information relating to a transport packet sequence number corresponding to the transport packet having its start portion stored in the second block section of the signal block, and x and y are integers such that x∃1 and y greater than 1. This enables a reproduction in the reproducing arrangement in a normal play mode using the first signal blocks and a reproduction in a trick play mode using the second signal blocks, in response to the detection of the information. indicating the groups comprising first signal blocks or second signal blocks respectively.
The recording arrangement as given in the opening paragraph may also be characterized in that the second block sections of all signal blocks in each first and second group of first and second signal blocks respectively comprise a third block section for storing identification information indicating whether the group comprises first signal blocks or second signal blocks. More specifically, the second block sections of a group of y signal blocks each comprise a third block section for storing sequence number information relating to a transport packet sequence number corresponding to the transport packet of which information is stored in said signal block.
Storing a packet sequence number has its advantages if an MPEG data stream is received having a constant bit or transport rate, and comprising a number of different video programs interleaved in the MPEG data stream. Generally, such data stream has a too high bit rate for recording the total data stream on the record carrier. Typically, the MPEG bit rate is 45 Mbps, whereas the record carrier typically records with a 25 Mbps bit rate. The recording arrangement now comprises a program selector for retrieving one video program and corresponding audio signal from the MPEG data stream so as to obtain the MPEG information signal for recording. As information corresponding to only one video program is included in a MPEG transport packet, such program selector selects only those transport packets from the MPEG data stream that comprise information corresponding to said only one video program. That means that some packets of the original MPEG data stream received are deleted. Upon reproduction however, an MPEG video signal in accordance with the MPEG standard, however now comprising only the one video program, should be regenerated or recreated. Such regenerated data stream should have the transport packets that were selected upon recording at the same location, that is in one or other way, dummy packets corresponding to the packets deleted upon recording must be inserted in the regenerated data stream. Upon recording a sequence number is added to each transport packet received, that is: also for the packets that will be deleted. The sequence numbers of the packets that are selected and stored is stored in the third block section of the signal blocks in which a transport packet is stored. Upon reproduction, a sequence of numbers is retrieved, where subsequent numbers will not necessarily be next higher numbers. In that situation one or more dummy packets must be inserted so as to regenerate the replica of the original MPEG data stream.
The recording arrangement as given in the opening paragraph can further be characterized in that the information signal is an MPEG information signal in accordance with an MPEG format, the MPEG information signal comprising subsequent transport packets, the recording arrangement comprising detection means for detecting the moment of receipt of the transport packets and for generating timing information for each transport packet received, the timing information for a transport packet corresponding to said moment of receipt of said transport packet, that the channel encoding means are adapted to each time store information included in x transport packets of the MPEG information signal in the second block sections of a group of y signal blocks of the channel signal, that the second block sections of at least those signal blocks in a group of y signal blocks that comprise the start portion of a transport packet comprise a third block section for storing the timing information for said transport packet having its start portion stored in the second block section of the signal block, and that x and y are integers such that x∃1 and y greater than 1.
More specifically, the second block sections of a group of y signal blocks each comprise a third block section for storing the timing information corresponding to the transport packet which has information stored in the second block section of said signal block.
Storing timing information corresponding to transport packet requires that the recording arrangement is provided with detection means for detecting the time of receipt of a transport packet. This measure has its advantages if an MPEG data stream is received having a variable bit rate, and comprising a number of different video programs interleaved in the MPEG data stream. As has been said above, generally, such data stream has a too high bit rate for recording the total data stream on the record carrier. The recording arrangement now comprises a program selector for retrieving one video program with its corresponding audio signal from the MPEG data stream so as to obtain the MPEG information signal for recording. As information corresponding to only one video program is included in a MPEG transport packet, such program selector selects only those transport packets from the MPEG data stream that comprise information corresponding to said only one video program. By detecting and storing the timing information corresponding to a transport packet, the reproducing arrangement will be capable of retrieving the timing information and recreating the MPEG information signal using said timing information.
It should be noted that the measures discussed above can be applied solely or in combination with one another in the recording arrangement. As a result, record carriers will be obtained having signal blocks stored in tracks on the record carrier, the signal blocks having a first block section which comprises a synchronization signal and a second block section which comprises a number of channel bytes, x transport packets of the MPEG information signal being stored in the second block sections of a group of y signal blocks of the channel signal. Further in accordance with the invention,
the second block section of at least the first signal block of the group of y signal blocks comprise a third block section for storing identification information identifying the signal block as being the first signal block of the group of y signal blocks, or
said identification information is sequence number information and the second block sections of a group of y signal blocks all comprise a third block section for storing sequence number information relating to the sequence numbers of the signal blocks, or
the second block sections of the signal blocks each comprise a third block section for storing identification information indicating whether the signal block comprise xe2x80x98normal playxe2x80x99 data or xe2x80x98trick modexe2x80x99 data, or
the second block sections of at least those signal blocks in a group of y signal blocks that comprises the start portion of a transport packet comprise a third block section for storing identification information relating to a transport packet sequence number corresponding to the transport packet having its start portion stored in the second block section of the signal block, or
the second block sections of at least those signal blocks in a group of y signal blocks that comprises the start portion of a transport packet comprise a third block section for storing the timing information for said transport packet having its start portion stored in the second block section of the signal block, or
third block sections comprise information resulting from a combination of one or more of the measures listed above.
It will be apparent that a reproducing arrangement will be needed which is adapted to each specific embodiment of the recording arrangement, so as to enable a reproduction of the MPEG information signal recorded on the record carrier. Such reproducing arrangement is the subject of the claims directed to the reproduction arrangement.
The invention also includes the method of transmitting timing critical data over an asynchronous channel without changing any of the critical timing information; in other words, to make the asynchronous channel transparent for the timing critical data. This is achieved, broadly speaking, by tagging one or more of the transmission units making up the data with timing information before sending it over the channel, and then using the tagged information to recreate the proper data timing at the other end of the channel. As an example, the data can be an MPEG information signal, and the channel a DVCR. But the invention is not limited to this application and can also be applied to asynchronous channels such as a computer network, a telephone network or a digital interface.
Those skilled in the art are hereby directed to the following references:
(1) European patent application no. 492,704 (PHN 13.546);
(2) European patent application no. 93.202.950 (PHN 14.241);
(3) European patent application no. 93.201.263 (PHN 14.449);
(4) Grand Alliance HDTV System Specification, Draft document, Feb. 22, 1994; and
(5) U.S. Pat. No. 5,142,421 (PHN 13.537).
The above references are hereby incorporated in whole by reference.